package org.example.brave.spring.webmvc;

import brave.SpanCustomizer;
import brave.internal.Nullable;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Adds application-tier data to an existing http span via {@link HandlerParser}. This also sets the
 * request property "http.route" so that it can be used in naming the http span.
 *
 * <p>Use this when you start traces at the servlet layer via {@link brave.servlet.TracingFilter}.
 */
public final class SpanCustomizingHandlerInterceptor implements HandlerInterceptor {
    /** Redefined from HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE added in Spring 3. */
    static final String BEST_MATCHING_PATTERN_ATTRIBUTE =
            "org.springframework.web.servlet.HandlerMapping.bestMatchingPattern";

    @Autowired(required = false)
    HandlerParser handlerParser = new HandlerParser();

    SpanCustomizingHandlerInterceptor() { // hide the ctor so we can change later if needed
    }

    /**
     * Parses the request and sets the "http.route" attribute so that the {@link TracingFilter} can
     * read it.
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object o) {
        Object span = request.getAttribute(SpanCustomizer.class.getName());
        if (span instanceof SpanCustomizer) {
            setHttpRouteAttribute(request);
            handlerParser.preHandle(request, o, (SpanCustomizer) span);
        }
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                           ModelAndView modelAndView) {
    }

    /** Sets the "error" attribute so that the {@link TracingFilter} can read it. */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response,
                                Object handler, Exception ex) {
        Object span = request.getAttribute(SpanCustomizer.class.getName());
        if (span instanceof SpanCustomizer) {
            setErrorAttribute(request, ex);
        }
    }

    /**
     * Sets the "error" attribute if not already set, so that the {@link TracingFilter} can read it.
     */
    static void setErrorAttribute(HttpServletRequest request, @Nullable Exception ex) {
        if (ex != null && request.getAttribute("error") == null) {
            request.setAttribute("error", ex);
        }
    }

    /**
     * Sets the "http.route" attribute from {@link #BEST_MATCHING_PATTERN_ATTRIBUTE} so that the
     * {@link TracingFilter} can read it.
     */
    static void setHttpRouteAttribute(HttpServletRequest request) {
        Object httpRoute = request.getAttribute(BEST_MATCHING_PATTERN_ATTRIBUTE);
        request.setAttribute("http.route", httpRoute != null ? httpRoute.toString() : "");
    }
}
